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[NaryReassoc] reassociate GEP for CSE
Summary: x = &a[i]; y = &a[i + j]; => y = x + j; along with some refactoring work such as extracting method findClosestMatchingDominator. Depends on D9786 which provides the ScalarEvolution::getGEPExpr interface. Test Plan: nary-gep.ll Reviewers: meheff, broune Reviewed By: broune Subscribers: jholewinski, llvm-commits Differential Revision: http://reviews.llvm.org/D9802 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237971 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -85,6 +85,7 @@
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/PatternMatch.h"
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@ -104,6 +105,10 @@ public:
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initializeNaryReassociatePass(*PassRegistry::getPassRegistry());
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}
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bool doInitialization(Module &M) override {
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DL = &M.getDataLayout();
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return false;
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}
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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@ -113,6 +118,7 @@ public:
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<ScalarEvolution>();
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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AU.setPreservesCFG();
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}
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@ -120,16 +126,49 @@ private:
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// Runs only one iteration of the dominator-based algorithm. See the header
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// comments for why we need multiple iterations.
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bool doOneIteration(Function &F);
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// Reasssociates I to a better form.
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Instruction *tryReassociateAdd(Instruction *I);
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// Reassociates I for better CSE.
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Instruction *tryReassociate(Instruction *I);
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// Reassociate GEP for better CSE.
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Instruction *tryReassociateGEP(GetElementPtrInst *GEP);
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// Try splitting GEP at the I-th index and see whether either part can be
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// CSE'ed. This is a helper function for tryReassociateGEP.
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//
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// \p IndexedType The element type indexed by GEP's I-th index. This is
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// equivalent to
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// GEP->getIndexedType(GEP->getPointerOperand(), 0-th index,
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// ..., i-th index).
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GetElementPtrInst *tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
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unsigned I, Type *IndexedType);
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// Given GEP's I-th index = LHS + RHS, see whether &Base[..][LHS][..] or
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// &Base[..][RHS][..] can be CSE'ed and rewrite GEP accordingly.
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GetElementPtrInst *tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
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unsigned I, Value *LHS,
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Value *RHS, Type *IndexedType);
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// Reassociate Add for better CSE.
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Instruction *tryReassociateAdd(BinaryOperator *I);
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// A helper function for tryReassociateAdd. LHS and RHS are explicitly passed.
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Instruction *tryReassociateAdd(Value *LHS, Value *RHS, Instruction *I);
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// Rewrites I to LHS + RHS if LHS is computed already.
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Instruction *tryReassociatedAdd(const SCEV *LHS, Value *RHS, Instruction *I);
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// Returns the closest dominator of \c Dominatee that computes
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// \c CandidateExpr. Returns null if not found.
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Instruction *findClosestMatchingDominator(const SCEV *CandidateExpr,
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Instruction *Dominatee);
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// GetElementPtrInst implicitly sign-extends an index if the index is shorter
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// than the pointer size. This function returns whether Index is shorter than
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// GEP's pointer size, i.e., whether Index needs to be sign-extended in order
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// to be an index of GEP.
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bool requiresSignExtension(Value *Index, GetElementPtrInst *GEP);
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DominatorTree *DT;
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ScalarEvolution *SE;
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TargetLibraryInfo *TLI;
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TargetTransformInfo *TTI;
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const DataLayout *DL;
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// A lookup table quickly telling which instructions compute the given SCEV.
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// Note that there can be multiple instructions at different locations
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// computing to the same SCEV, so we map a SCEV to an instruction list. For
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@ -149,6 +188,7 @@ INITIALIZE_PASS_BEGIN(NaryReassociate, "nary-reassociate", "Nary reassociation",
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_END(NaryReassociate, "nary-reassociate", "Nary reassociation",
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false, false)
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@ -163,6 +203,7 @@ bool NaryReassociate::runOnFunction(Function &F) {
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DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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SE = &getAnalysis<ScalarEvolution>();
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TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
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TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
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bool Changed = false, ChangedInThisIteration;
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do {
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@ -172,26 +213,36 @@ bool NaryReassociate::runOnFunction(Function &F) {
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return Changed;
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}
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// Whitelist the instruction types NaryReassociate handles for now.
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static bool isPotentiallyNaryReassociable(Instruction *I) {
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switch (I->getOpcode()) {
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case Instruction::Add:
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case Instruction::GetElementPtr:
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return true;
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default:
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return false;
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}
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}
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bool NaryReassociate::doOneIteration(Function &F) {
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bool Changed = false;
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SeenExprs.clear();
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// Traverse the dominator tree in the depth-first order. This order makes sure
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// all bases of a candidate are in Candidates when we process it.
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// Process the basic blocks in pre-order of the dominator tree. This order
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// ensures that all bases of a candidate are in Candidates when we process it.
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for (auto Node = GraphTraits<DominatorTree *>::nodes_begin(DT);
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Node != GraphTraits<DominatorTree *>::nodes_end(DT); ++Node) {
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BasicBlock *BB = Node->getBlock();
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for (auto I = BB->begin(); I != BB->end(); ++I) {
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// Skip vector types which are not SCEVable.
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if (I->getOpcode() == Instruction::Add && !I->getType()->isVectorTy()) {
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if (Instruction *NewI = tryReassociateAdd(I)) {
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if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(I)) {
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if (Instruction *NewI = tryReassociate(I)) {
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Changed = true;
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SE->forgetValue(I);
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I->replaceAllUsesWith(NewI);
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RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
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I = NewI;
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}
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// We should add the rewritten instruction because tryReassociateAdd may
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// have invalidated the original one.
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// Add the rewritten instruction to SeenExprs; the original instruction
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// is deleted.
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SeenExprs[SE->getSCEV(I)].push_back(I);
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}
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}
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@ -199,7 +250,168 @@ bool NaryReassociate::doOneIteration(Function &F) {
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return Changed;
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}
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Instruction *NaryReassociate::tryReassociateAdd(Instruction *I) {
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Instruction *NaryReassociate::tryReassociate(Instruction *I) {
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switch (I->getOpcode()) {
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case Instruction::Add:
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return tryReassociateAdd(cast<BinaryOperator>(I));
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case Instruction::GetElementPtr:
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return tryReassociateGEP(cast<GetElementPtrInst>(I));
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default:
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llvm_unreachable("should be filtered out by isPotentiallyNaryReassociable");
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}
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}
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// FIXME: extract this method into TTI->getGEPCost.
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static bool isGEPFoldable(GetElementPtrInst *GEP,
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const TargetTransformInfo *TTI,
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const DataLayout *DL) {
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GlobalVariable *BaseGV = nullptr;
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int64_t BaseOffset = 0;
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bool HasBaseReg = false;
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int64_t Scale = 0;
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getPointerOperand()))
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BaseGV = GV;
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else
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HasBaseReg = true;
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gep_type_iterator GTI = gep_type_begin(GEP);
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for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I, ++GTI) {
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if (isa<SequentialType>(*GTI)) {
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int64_t ElementSize = DL->getTypeAllocSize(GTI.getIndexedType());
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if (ConstantInt *ConstIdx = dyn_cast<ConstantInt>(*I)) {
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BaseOffset += ConstIdx->getSExtValue() * ElementSize;
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} else {
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// Needs scale register.
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if (Scale != 0) {
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// No addressing mode takes two scale registers.
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return false;
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}
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Scale = ElementSize;
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}
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} else {
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StructType *STy = cast<StructType>(*GTI);
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uint64_t Field = cast<ConstantInt>(*I)->getZExtValue();
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BaseOffset += DL->getStructLayout(STy)->getElementOffset(Field);
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}
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}
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return TTI->isLegalAddressingMode(GEP->getType()->getElementType(), BaseGV,
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BaseOffset, HasBaseReg, Scale);
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}
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Instruction *NaryReassociate::tryReassociateGEP(GetElementPtrInst *GEP) {
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// Not worth reassociating GEP if it is foldable.
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if (isGEPFoldable(GEP, TTI, DL))
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return nullptr;
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gep_type_iterator GTI = gep_type_begin(*GEP);
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for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I) {
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if (isa<SequentialType>(*GTI++)) {
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if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I - 1, *GTI)) {
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return NewGEP;
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}
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}
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}
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return nullptr;
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}
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bool NaryReassociate::requiresSignExtension(Value *Index,
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GetElementPtrInst *GEP) {
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unsigned PointerSizeInBits =
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DL->getPointerSizeInBits(GEP->getType()->getPointerAddressSpace());
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return cast<IntegerType>(Index->getType())->getBitWidth() < PointerSizeInBits;
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}
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GetElementPtrInst *
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NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
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Type *IndexedType) {
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Value *IndexToSplit = GEP->getOperand(I + 1);
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if (SExtInst *SExt = dyn_cast<SExtInst>(IndexToSplit))
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IndexToSplit = SExt->getOperand(0);
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if (AddOperator *AO = dyn_cast<AddOperator>(IndexToSplit)) {
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// If the I-th index needs sext and the underlying add is not equipped with
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// nsw, we cannot split the add because
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// sext(LHS + RHS) != sext(LHS) + sext(RHS).
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if (requiresSignExtension(IndexToSplit, GEP) && !AO->hasNoSignedWrap())
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return nullptr;
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Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
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// IndexToSplit = LHS + RHS.
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if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I, LHS, RHS, IndexedType))
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return NewGEP;
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// Symmetrically, try IndexToSplit = RHS + LHS.
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if (LHS != RHS) {
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if (auto *NewGEP =
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tryReassociateGEPAtIndex(GEP, I, RHS, LHS, IndexedType))
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return NewGEP;
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}
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}
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return nullptr;
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}
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GetElementPtrInst *
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NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
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Value *LHS, Value *RHS,
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Type *IndexedType) {
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// Look for GEP's closest dominator that has the same SCEV as GEP except that
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// the I-th index is replaced with LHS.
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SmallVector<const SCEV *, 4> IndexExprs;
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for (auto Index = GEP->idx_begin(); Index != GEP->idx_end(); ++Index)
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IndexExprs.push_back(SE->getSCEV(*Index));
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// Replace the I-th index with LHS.
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IndexExprs[I] = SE->getSCEV(LHS);
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const SCEV *CandidateExpr = SE->getGEPExpr(
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GEP->getSourceElementType(), SE->getSCEV(GEP->getPointerOperand()),
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IndexExprs, GEP->isInBounds());
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auto *Candidate = findClosestMatchingDominator(CandidateExpr, GEP);
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if (Candidate == nullptr)
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return nullptr;
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PointerType *TypeOfCandidate = dyn_cast<PointerType>(Candidate->getType());
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// Pretty rare but theoretically possible when a numeric value happens to
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// share CandidateExpr.
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if (TypeOfCandidate == nullptr)
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return nullptr;
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// NewGEP = (char *)Candidate + RHS * sizeof(IndexedType)
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uint64_t IndexedSize = DL->getTypeAllocSize(IndexedType);
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Type *ElementType = TypeOfCandidate->getElementType();
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uint64_t ElementSize = DL->getTypeAllocSize(ElementType);
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// Another less rare case: because I is not necessarily the last index of the
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// GEP, the size of the type at the I-th index (IndexedSize) is not
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// necessarily divisible by ElementSize. For example,
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//
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// #pragma pack(1)
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// struct S {
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// int a[3];
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// int64 b[8];
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// };
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// #pragma pack()
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//
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// sizeof(S) = 100 is indivisible by sizeof(int64) = 8.
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//
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// TODO: bail out on this case for now. We could emit uglygep.
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if (IndexedSize % ElementSize != 0)
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return nullptr;
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// NewGEP = &Candidate[RHS * (sizeof(IndexedType) / sizeof(Candidate[0])));
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IRBuilder<> Builder(GEP);
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Type *IntPtrTy = DL->getIntPtrType(TypeOfCandidate);
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if (RHS->getType() != IntPtrTy)
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RHS = Builder.CreateSExtOrTrunc(RHS, IntPtrTy);
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if (IndexedSize != ElementSize) {
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RHS = Builder.CreateMul(
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RHS, ConstantInt::get(IntPtrTy, IndexedSize / ElementSize));
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}
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GetElementPtrInst *NewGEP =
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cast<GetElementPtrInst>(Builder.CreateGEP(Candidate, RHS));
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NewGEP->setIsInBounds(GEP->isInBounds());
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NewGEP->takeName(GEP);
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return NewGEP;
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}
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Instruction *NaryReassociate::tryReassociateAdd(BinaryOperator *I) {
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Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
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if (auto *NewI = tryReassociateAdd(LHS, RHS, I))
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return NewI;
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@ -236,22 +448,34 @@ Instruction *NaryReassociate::tryReassociatedAdd(const SCEV *LHSExpr,
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if (Pos == SeenExprs.end())
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return nullptr;
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auto &LHSCandidates = Pos->second;
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// Look for the closest dominator LHS of I that computes LHSExpr, and replace
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// I with LHS + RHS.
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//
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// Because we traverse the dominator tree in the pre-order, a
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auto *LHS = findClosestMatchingDominator(LHSExpr, I);
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if (LHS == nullptr)
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return nullptr;
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Instruction *NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
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NewI->takeName(I);
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return NewI;
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}
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Instruction *
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NaryReassociate::findClosestMatchingDominator(const SCEV *CandidateExpr,
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Instruction *Dominatee) {
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auto Pos = SeenExprs.find(CandidateExpr);
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if (Pos == SeenExprs.end())
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return nullptr;
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auto &Candidates = Pos->second;
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// Because we process the basic blocks in pre-order of the dominator tree, a
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// candidate that doesn't dominate the current instruction won't dominate any
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// future instruction either. Therefore, we pop it out of the stack. This
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// optimization makes the algorithm O(n).
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while (!LHSCandidates.empty()) {
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Instruction *LHS = LHSCandidates.back();
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if (DT->dominates(LHS, I)) {
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Instruction *NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
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NewI->takeName(I);
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return NewI;
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}
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LHSCandidates.pop_back();
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while (!Candidates.empty()) {
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Instruction *Candidate = Candidates.back();
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if (DT->dominates(Candidate, Dominatee))
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return Candidate;
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Candidates.pop_back();
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}
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return nullptr;
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}
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77
test/Transforms/NaryReassociate/NVPTX/nary-gep.ll
Normal file
77
test/Transforms/NaryReassociate/NVPTX/nary-gep.ll
Normal file
@ -0,0 +1,77 @@
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; RUN: opt < %s -nary-reassociate -S | FileCheck %s
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target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
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target triple = "nvptx64-unknown-unknown"
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declare void @foo(float*)
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; foo(&a[i]);
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; foo(&a[i + j]);
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; =>
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; t = &a[i];
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; foo(t);
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; foo(t + j);
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define void @reassociate_gep(float* %a, i64 %i, i64 %j) {
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; CHECK-LABEL: @reassociate_gep(
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%1 = add i64 %i, %j
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%2 = getelementptr float, float* %a, i64 %i
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; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i64 %i
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call void @foo(float* %2)
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; CHECK: call void @foo(float* [[t1]])
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%3 = getelementptr float, float* %a, i64 %1
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; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 %j
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call void @foo(float* %3)
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; CHECK: call void @foo(float* [[t2]])
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ret void
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}
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; foo(&a[sext(j)]);
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; foo(&a[sext(i +nsw j)]);
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; =>
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; t = &a[sext(j)];
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; foo(t);
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; foo(t + sext(i));
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define void @reassociate_gep_nsw(float* %a, i32 %i, i32 %j) {
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; CHECK-LABEL: @reassociate_gep_nsw(
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%1 = add nsw i32 %i, %j
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%idxprom.1 = sext i32 %1 to i64
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%idxprom.j = sext i32 %j to i64
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%2 = getelementptr float, float* %a, i64 %idxprom.j
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; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i64 %idxprom.j
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call void @foo(float* %2)
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; CHECK: call void @foo(float* [[t1]])
|
||||
%3 = getelementptr float, float* %a, i64 %idxprom.1
|
||||
; CHECK: [[sexti:[^ ]+]] = sext i32 %i to i64
|
||||
; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 [[sexti]]
|
||||
call void @foo(float* %3)
|
||||
; CHECK: call void @foo(float* [[t2]])
|
||||
ret void
|
||||
}
|
||||
|
||||
; Do not split the second GEP because sext(i + j) != sext(i) + sext(j).
|
||||
define void @reassociate_gep_no_nsw(float* %a, i32 %i, i32 %j) {
|
||||
; CHECK-LABEL: @reassociate_gep_no_nsw(
|
||||
%1 = add i32 %i, %j
|
||||
%2 = getelementptr float, float* %a, i32 %j
|
||||
; CHECK: getelementptr float, float* %a, i32 %j
|
||||
call void @foo(float* %2)
|
||||
%3 = getelementptr float, float* %a, i32 %1
|
||||
; CHECK: getelementptr float, float* %a, i32 %1
|
||||
call void @foo(float* %3)
|
||||
ret void
|
||||
}
|
||||
|
||||
define void @reassociate_gep_128(float* %a, i128 %i, i128 %j) {
|
||||
; CHECK-LABEL: @reassociate_gep_128(
|
||||
%1 = add i128 %i, %j
|
||||
%2 = getelementptr float, float* %a, i128 %i
|
||||
; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i128 %i
|
||||
call void @foo(float* %2)
|
||||
; CHECK: call void @foo(float* [[t1]])
|
||||
%3 = getelementptr float, float* %a, i128 %1
|
||||
; CHECK: [[truncj:[^ ]+]] = trunc i128 %j to i64
|
||||
; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 [[truncj]]
|
||||
call void @foo(float* %3)
|
||||
; CHECK: call void @foo(float* [[t2]])
|
||||
ret void
|
||||
}
|
Loading…
Reference in New Issue
Block a user